[Effects of exercise and calcium-intake on bone hardness and bone constituents in aged mice]

Effects of exercise and differing calcium intakes on bone hardness and bone constituents were examined using mice (40 weeks old) in successive stages of senescence to contribute to our understanding of preventive measures against osteoporosis. In the present study, the mice were divided into four groups, combinations of stock diet (Ca: 1.25 g/100 g) or low Ca diet (Ca: 0.15 g/100 g), with or without physical exercise (forced exercise, 40 min/day at a velocity of 12 m/min) and maintained in their respective conditions for 16 weeks. Autopsies were performed or representative mice every four weeks (44, 48, 52, 56 weeks old). The obtained results are summarized as follows: 1) In female mice highest values for femoral bone weight were observed after 48 weeks in the mice exposed to forced exercise and on a stock diet and had a significant difference from the other groups. No difference was observed in male mice. 2) Bone hardness had a tendency to be reduced with age in all groups. The velocity of diminution was small in the mice kept on stock diet as compared to those on a low Ca diet. The highest bone hardness was observed in the mice kept in forced exercise and stock diet group at every stage. 3) Bone constituents, Ca, P and hydroxyproline, showed no differences in concentration per weight of bone. But higher total content in the femur was obtained in the mice kept on a stock diet. 4) No differences in concentration of serum calcitonin and parathormone were seen in every group of male mice.(ABSTRACT TRUNCATED AT 250 WORDS)